62 ETHEL BROWNE HARVEY 
The same explanation holds for the two Banasas, one of which, 
B. dimidiata has a haploid number of 8 (like Thyanta custator) 
and the other, B. calva has a haploid number of 13 (like T. 
calceata, except that X is single). Euschistus crassus differs 
from five other species of the same genus which have the type 
number, in having one less. A comparison of Foot and Stro- 
bell’s figures of this species with their figures of the other species 
would indicate that a union of two large chromosomes has taken 
place. That the chromosome number does change by the fusion 
or splitting of chromosomes is shown by the Notonectidae. In 
three species (Browne, ’16) there are 13 chromosomes, including 
two small ones, and in two species there are 12 chromosomes 
including only one small one. Ina sixth species, N. insulata, the 
second small chromosome may be seen attached to another chro- 
mosome in the first division of some cells, while in other cells it 
is free, whereas in the second division it is permanently fused 
with the other chromosome. . The d-chromosome of Nezara may 
also represent a stage in splitting or fusion, as suggested by 
Wilson. The fact that the X chromcsome may consist of two 
or more parts, as in Syromastes, Phylloxera and some Reduvioids, 
would indicate that other chromosomes whose identity is not so 
easily established, may also split into two or more parts. 
The type number for the Diptera is 6, including XY which 
are, however, not always distinguishable. There is a decided 
tendency for the chromosomes to fuse, especially among the 
Drosophilas, most of which have 4 chromosomes, and the Culi- 
cidae, most of which have 3. In Anopheles punctipennis, (Ste- 
vens, 711), the X and Y are seen to be attached toanother pair 
in the diploid groups. Metz, ’16, has made a careful study of 
the chromosomes in the genus Drosophila, and has shown that— 
many groups having a larger number of chromosomes contain 
rod shaped ones which are represented in groups with a smaller 
number by half as many V-shaped ones, two rods uniting to 
forma V. When the linkage groups in other species of Droso- 
phila have been worked out as extensively as in D. melanogaster, 
it may be possible to establish the relation between chromo- 
